The structure-function relationships of DNase will be investigated from several angles. First, the study of the crucial portion of the enzyme molecule involved in the catalytic action. The knowledge of the essential residues will be probed via chemical modifications or affinity labelling. The residues responsible for the overall conformation of the enzyme will be investigated by the use of proteolytic enzymes. Recent studies, which show the importance of the COOH-terminal residues will be extended to correlate the inter portion of the COOH-terminal region with enzyme activity. Carboxypeptidase Y, which can hydrolyze many amino acid residues, including proline, from the COOH-terminus of a protein, will be used in the study. Efforts will also be placed on the regain of activity by mixing the shortened polypeptide chain of the enzyme with synthetic peptides of the COOH-terminal region. Second objective is to focus on the mechanism of enzyme action in terms of its substrate specificity and the complex formation between the metal ions and the substrate. The recent discovery that DNase has the ability to hydrolyze thymidine 3', 5'-di-p-nitrophenyl phosphate has prompted many lines of research, including the measurements of the dissociation constants of metal ions with this new substrate, the synthesis of p-nitro-phenyl esters of other nucleotides, reexamination of products formed by the action of DNase on DNA in order to explain the reversed specificity between DNA and the p-nitro-phenyl ester as substrates, as well as the synthesis of substrate or product analogues for affinity labelling. Phosphodiesterases, including snake venom phosphodiesterase, spleen acid DNase and pancreatic phosphosphodiesterase, will also be studied. This may add to the knowledge as how H2O molecule is added to split a phosphodiester bond of the DNA type. Finally, the elucidation of the structure of those enzymes in comparison with that of pancreatic DNase will also be included in the investigation.